1. Field of the Invention
The present invention generally relates to computer-aided circuit design systems, and more particularly, to an electrical rules checker system and method for placing clock buffers in a datapath stack.
2. Discussion of the Related Art
Integrated circuits (ICs) are electrical circuits comprising of transistors, resistors, capacitors, and other components on a single semiconductor xe2x80x9cchipxe2x80x9d on which the components are interconnected to perform a variety of functions. Typical examples of ICs include, for example, microprocessors, programmable logic devices (PLDs), electrically erasable programmable read only memory (EEPROM) devices, random access memory (RAM) devices, operational amplifiers and voltage regulators. A circuit designer typically designs the IC by creating a circuit schematic indicating the electrical components and their interconnections. Often, designs are simulated by computer to verify functionality and to ensure that performance goals are satisfied.
In electrical device engineering, the design and analysis work involved in producing electronic devices is often performed using electronic computer-aided design (E-CAD) tools. As will be appreciated, electronic devices include analog, digital, mixed hardware, optical, electro-mechanical, and a variety of other electrical devices. The design and subsequent simulation of any circuit, very large scale integration (VLSI) chip, or other electrical device via E-CAD tools allows a circuit to be thoroughly tested and often eliminates the need for building a prototype. Thus, today""s sophisticated E-CAD tools may enable the circuit manufacturer to go directly to the manufacturing stage without having to perform costly, time consuming prototyping.
In order to perform the simulation and analysis of a hardware device, E-CAD tools utilize an electronic representation of the hardware device. A xe2x80x9cnetlistxe2x80x9d is one common representation of a hardware device that includes the circuit. As will be appreciated by those skilled in the art of hardware device design, a xe2x80x9cnetlistxe2x80x9d is a detailed circuit specification used by logic synthesizers, circuit simulators and other circuit design optimization tools. A netlist typically comprises a list of circuit components and the interconnections between those components.
The two forms of a netlist are the flat netlist and the hierarchical netlist. Often, a netlist will contain a number of circuit xe2x80x9cmodulesxe2x80x9d which are used repetitively throughout the larger circuit. A flat netlist will contain multiple copies of the circuit modules essentially containing no boundary differentiation between the circuit modules and other components in the device. By way of analogy, one graphical representation of a flat netlist is simply the schematic of the circuit device.
In contrast, a hierarchical netlist will only maintain one copy of a circuit module, which may be used in multiple locations. By way of analogy, one graphical representation of a hierarchical netlist would show the basic and/or non-repetitive devices in schematic form and the more complex and/or repetitive circuit modules would be represented by xe2x80x9cblack boxes.xe2x80x9d As will be appreciated by those skilled in the art, a black box is a system or component where the inputs, outputs, and general function are known, but the contents of which are not shown. These xe2x80x9cblack boxxe2x80x9d representations, hereinafter called xe2x80x9cmodules,xe2x80x9d will mask the complexities therein, typically showing only input/output ports.
An IC design can be represented at different levels of abstraction, such as at the register-transfer level (RTL) and the at logic level, using a hardware description language (HDL). VHDL(copyright) and Verilog(copyright) are examples of HDL languages. At any abstraction level, an IC design is specified using behavioral or structural descriptions, or a mix of both. At the logical level, the behavioral description is specified using Boolean equations. The structural description is represented as a netlist of primitive cells. Examples of primitive cells are, among others, full-adders, logic gates, latches, and flip flops.
Set forth above is some very basic information regarding integrated circuits and circuit schematics that are represented in netlists. Systems are presently known that use the information provided in netlists to evaluate circuit timing and other related parameters. More specifically, systems are known that perform a timing analysis of circuits using netlist files. Although the operational specifics may vary from system to system, generally, such systems operate by identifying certain critical timing paths, then evaluating the circuit to determine whether timing violations may occur through the critical paths. As is known, timing specifications may be provided to such systems by way of a configuration file.
FIG. 1A is a block diagram illustrating a prior art static timing analyzer system that illustrates the basic informational flow in such a system and that is generally denoted by reference numeral 2. Specifically, one such system 2 is marketed under the name PathMill(copyright). FIG. 1 illustrates the informational flow in such a system 2. At the center of the diagram is a static timing analyzer 10, (i.e., the PathMill(copyright) program). Surrounding this block 10 are a number of other blocks that represent various input and output files and/or information.
More particularly, the static timing analyzer 10 may utilize a configuration file 12, a file of timing models 14, one or more netlist file(s) 16, a technology file 18, and a parasitics file 20, for various input information. In addition, the static timing analyzer 10 may generate a number of different output files or other output information, including a critical path report 22, a runtime log file 24, an error report 26, a software interface file 28, and a SPICE netlist 30. When started, the static timing analyzer 10 first processes the input netlist file(s) 16, the technology file 18, and the configuration file 12. The information from these files is subsequently used for performing path analyses. Since the functions and operation of static timing analyzer 10 are generally well known, they need not be discussed in detail herein.
While tools such as these are useful for the design verification process after layout, there are various shortcomings in the static timing analyzer 10, and other similar products. These shortcomings include, but are not limited to, the ability to identify appropriate locations and place clock buffers in a datapath stack. Typically, the placing of clock buffers in a datapath stack involves a single trace inside of a datapath macro at a consistent location. A datapath macro is a logical representation of logic and physical characteristics of a circuit element, and a datapath stack is a collection of datapath macros. Then, a trace is applied through the datapath stack to connect to the clock. Currently, this technique is not feasible due to the size and density of large memory arrays (i.e. latch arrays) that are now incorporated in the current IC technology. A lack of space between the datapath macros and a memory array is illustrated in FIG. 1B with the datapath blocks 32 and 34 being very compressed to the memory arrays 33.
Manually placing and connecting clock buffers on the artwork to the affected signals could correct some clocking errors. However, this is extremely imprecise and labor intensive and thus, few clock buffers are placed manually. Consequently, there is a heretofore unaddressed need existing in the industry for a way to address the aforementioned deficiencies and inadequacy.
The present invention provides a clock buffer placement system and method for placing clock buffers in a datapath stack. Briefly described, in architecture, the system can be implemented as follows. The clock buffer placement system has logic that positions at least one track beside the datapath stack in a netlist, and logic that identifies the location at which a clock buffer is needed in the at least one track. Then, a logic modifies the netlist by connecting the at least one datapath macro to the clock buffer on the at least one track.
The invention can also be viewed as providing one or more methods for placing clock buffers in a datapath stack. In this regard, one such method can be summarized by the following steps: (1) positioning at least one track beside the datapath stack in a netlist; (2) identifying a location at which a clock buffer is needed in at least one track; and (3) modifying the netlist by connecting at least one datapath macro to the clock buffer on the at least one track.